The invention relates to formulations that are applied to the skin to reduce the amount of solar ultraviolet radiation received by the skin. More particularly, the invention relates to formulations containing waterborne polyurethane polymers that impart several beneficial properties to topical formulations, including inter alia, water proofing, reduction in the migration of the formulation across the wearer's skin, and reduction of the penetration of the active ingredients of the formulation into the wearer's stratum corneum.
It is now generally recognized that exposure to solar radiation can have adverse health consequences, sometimes not appearing until several years following the exposure. Of course, the immediately appearing sunburn from an overexposure can itself be a serious acute health problem.
Many products are available to reduce the amount of solar ultraviolet radiation received by the skin during exposure to the sun's rays. Typical product formulations are lotions, creams, ointments or gels containing chemical and/or physical barriers to ultraviolet transmission. These vary considerably in their abilities to protect the skin against the physical and biochemical effects of ultraviolet radiation. Many conventional cosmetic cream and lotion compositions are described, for example, in Sagarin, Cosmetics Science and Technology, 2nd Edition, Volume 1, Wiley Interscience (1972), and Encyclopedia of Chemical Technology, Third Edition, Volume 7.
Earlier sunscreening formulations were designed to protect against sunburn from a limited solar exposure period, while transmitting sufficient radiation to permit skin tanning. However, the current focus is on eliminating as much ultraviolet radiation exposure as possible, it being recognized that skin tanning, while esthetically pleasing to some, is a clear indication of tissue damage from overexposure to solar radiation. It has been recently discovered that any amount of unprotected exposure can potentially cause immune system suppression and lead to future health problems, such as skin carcinomas and other dermatological disorders.
The SPF (Sun Protection Factor) rating system has been developed to provide consumer guidance in selecting suitable sunscreens for any given outdoor activity. In general, the SPF number approximately corresponds to the multiple of time during which the properly applied sunscreen will prevent obvious reddening of the skin, over the exposure time that causes unprotected skin to exhibit reddening. Thus, if an SPF 8 sunscreen formulation has been properly applied, a person should be able to remain in the sun without visible effects for eight times the usual unprotected duration. Of course, the duration of unprotected exposure which produces a visible effect on the skin varies from one individual to another, due to differences in their skin cells. Currently popular are high-SPF “sunblocker” products, having SPF values of at least 30.
Most of the commercially available sunscreen formulations are not well suited for use by those engaged in strenuous outdoor activities, such as construction work, gardening, athletic events and many others, due to the tendency for perspiration from the body to interact with the applied formulation. For example, perspiration, or moisture from other sources, including rain, can cause sunscreen active ingredients and other irritating components of the formulation to enter the eyes and cause discomfort. It is also frequently detrimental, particularly in activities such as tennis which require a reliable grip on equipment, to have an applied sunscreen formulation remain lubricious after application or become lubricious when mixed with perspiration or other moisture.
It is also advantageous to have a suncare formulation that is waterproof. Waterproof formulations allow the user to engage in activities such as swimming while still being protected against ultraviolet radiation. Hydrophobic materials typically serve as waterproofing agents that impart film forming and waterproofing characteristics to an emulsion. However, there is still a need for products having physical attributes that display improved waterproof performance, that have a reduction in migration of the formulation across the formulation wearer's skin, and have a reduction in the penetration of the active ingredients into the formulation wearer's skin.
A sunscreen product that has been available for several years, but which does not exhibit disadvantages such as the foregoing, is sold by Schering-Plough HealthCare Products, Inc., Memphis, Tenn. U.S.A. as COPPERTONE.RTM. SPORT.RTM. SPF 30 lotion. This product contains the active ingredients octyl salicylate, octyl methoxycinnamate and oxybenzone, totaling 17.5 weight percent of the formulation, and is an oil-in-water emulsion formulated with 1.5 weight percent of a fumed silica having a hydrophobic surface treatment. It is thought that the silica serves to immobilize the active agents in the internal phase of the formulation and inhibit their migration under the influence of skin oils and/or external moisture. The product also has a very desirable “dry” feel as it is being applied, quite unlike the very liquid nature of the usual lotion which does not contain particulate ingredients other than those approved for use as sunscreen active ingredients.
Not with standing the foregoing, there still exists a need for a waterproof formulation that exhibits beneficial properties such as a decreased partitioning of the formulation into the wearer's stratum corneum and a reduction in the migration of the sunscreen active agents across the wearers skin upon topical application of the formulation.